Components for medical circuits

ABSTRACT

An expiratory limb is provided that is configured to remove humidified gases from a patient and configured to provide improved drying performance by providing a tailored temperature profile along the limb. Limbs for providing humidified gases to and/or removing humidified gases from a patient are also provided, the limbs having improved gas residence time at constant volumetric flow rate. The improved residence time can be achieved by providing a limb comprising multiple lumens.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/777,438, entitled “COMPONENTS FOR MEDICAL CIRCUIT,” filed Sep. 15,2015, which is a 371 national phase of PCT Application No.PCT/NZ2014/000039, entitled “COMPONENTS FOR MEDICAL CIRCUITS,” filedMar. 14, 2014, which claims the benefit of U.S. Provisional ApplicationNo. 61/790,424, entitled “DRYING EXPIRATORY LIMB WITH TAILOREDTEMPERATURE PROFILE,” filed Mar. 15, 2013, U.S. Provisional ApplicationNo. 61/789,754, entitled “DRYING EXPIRATORY LIMB WITH TAILOREDTEMPERATURE PROFILE AND MULTI-LUMEN CONFIGURATION,” filed Mar. 15, 2013,and U.S. Provisional Application No. 61/925,099, entitled “COMPONENTSFOR MEDICAL CIRCUITS,” filed Jan. 8, 2014, each of which is incorporatedby reference herein in its entirety.

BACKGROUND Field

This disclosure relates generally to components for medical circuits,and in particular to components for medical circuits providinghumidified gases to and/or removing humidified gases from a patient,such as in obstructive sleep apnea, neonatal, respiratoryhumidification, and surgical humidification systems includinginsufflation systems.

Description of Related Art

In medical circuits, various components transport naturally orartificially humidified gases to and from patients. For example, in somebreathing circuits such as CPAP (continuous positive airway pressure) orassisted-breathing circuits, gases inhaled by a patient are deliveredfrom a heater-humidification unit through an inspiratory limb to apatient interface, such as a mask. As another example, surgicalhumidification limbs can deliver humidified gas (commonly CO₂) into theabdominal cavity in insufflation circuits. This can help prevent “dryingout” of the patient's internal organs, and can decrease the amount oftime needed for recovery from surgery.

In these medical applications, the gases are preferably delivered in acondition having humidity near saturation level and at close to bodytemperature (usually at a temperature between 33° C. and 37° C.).Condensation or “rain-out” can form on the inside surfaces of componentsas high humidity gases cool. A need remains for components that allowfor improved humidification and condensate management in medicalcircuits. Accordingly, an object of certain components and methodsdescribed herein is to ameliorate one or more of the problems of priorart systems, or at least to provide the public with a useful choice.

SUMMARY

Aspects of this disclosure relate to limbs for use in medical circuits.Limb is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (that is, it is not tobe limited to a special or customized meaning) and includes, withoutlimitation, tubes, conduits, and device components for transportinggases. The limbs disclosed herein can be applied in a variety ofapplications that would benefit from increasing the residence time of agas flow (that is, the average length of time during which a volume ofgas is in the limb).

Certain embodiments of this disclosure relate to an expiratory limbleading away from a patient where the absolute humidity and dew point ofthe gas stream flowing away from the patient interface is reduced in atailored and controlled fashion to eliminate condensation. Thisapplication is suitable for several medical environments including,without limitation, respiratory humidification and neonatalapplications. When used in applications that transfer humidified airaway from a patient, certain limbs described herein are capable ofrealizing reduced dew points over commercial products, such as Evaqua 2™conduits (Fisher & Paykel Healthcare Ltd., Auckland, New Zealand).

Additional embodiments of this disclosure relate to humidifying a gasstream flowing towards the patient. In particular, at least oneembodiment relates to a limb suitable for use in a humidification unit.This application is suitable for several medical environments including,without limitation, obstructive sleep apnea (such as CPAP) and surgicalhumidification applications. When used in applications that transferhumidified air to a patient, certain limbs described herein are capableof realizing increased dew points over previous commercial products.

The systems, methods and devices described herein have innovativeaspects, no single one of which is indispensable or solely responsiblefor their desirable attributes. Without limiting the scope of theclaims, some of the advantageous features will now be summarized.

In general, an expiratory limb is configured to dry a gas as it passesthrough the expiratory limb prior to reaching a ventilator. Theexpiratory limb can be configured to dry the gas sufficiently to reduceor eliminate condensation in the ventilator. Drying can be limited atleast in part by a surface area of the limb and/or a residence time ofthe gas in the expiratory limb at constant volumetric flow rate. Certainembodiments include the realization that it may be advantageous toprovide a drying expiratory limb that provides a tailored temperatureprofile of the gas along the expiratory limb to increase drying, toreduce or prevent rain out along the limb, and/or to reduce or preventcondensation in the ventilator.

In some embodiments, an improved or optimized drying of the gas within adrying expiratory limb is accomplished by controlling the temperature ofthe gas as it passes along the drying expiratory limb to maintain adifference between the gas temperature and its dew point temperatureapproximately constant. In some embodiments, this temperature differenceis less than about 2° C., less than about 1.5° C., or between about 0.9°C. and about 1° C. In some embodiments, an improved or optimized dryingof the gas within the drying expiratory limb is accomplished by keepingthe relative humidity of the gas between about 90% and about 99%,between about 95% and about 99%, or between about 95% and about 97%. Insome embodiments, this may be accomplished by keeping the dew pointtemperature and absolute humidity approximately linear along the lengthof the expiratory limb. In some embodiments, the temperature drop of thegas from the beginning of the limb to about the first 300 mm or 400 mmof the drying expiratory limb is less than 0.01° C./mm or between 0°C./mm and about 0.009° C./mm and the total temperature drop across theexpiratory limb length is less than about 10° C., or between about 3° C.and about 10° C. Accordingly, the drying expiratory limbs andtemperature control mechanisms disclosed herein can be configured totailor a temperature profile of the gas to increase or optimize dryingof the gas, to reduce or eliminate rain out in the limb, and/or toreduce or eliminate condensation in the ventilator. In some embodiments,a drying expiratory limb is disclosed that provides an optimal drying ofa gas where the optimal drying is where no condensation occurs in thelimb or in the ventilator through a tailored temperature controlprocess.

Some embodiments provide for a drying expiratory limb for use in arespiratory circuit which can include a wall having a first end and asecond end separated by an expiratory limb length. The wall defines aspace within and at least a part of said wall comprises a breathablematerial configured to allow transmission of water vapor butsubstantially prevent transmission of liquid water. The dryingexpiratory limb includes a first opening in the first end of the wall,the first opening configured to receive a gas at a first temperature anda first relative humidity. The drying expiratory limb includes a secondopening in the second end of the wall configured to allow the gas toexit the drying expiratory limb, the gas having a second temperature anda second relative humidity upon exiting the drying expiratory limb. Thedrying expiratory limb is configured such that a difference between atemperature of the gas and a dew point temperature of the gas along thedrying expiratory limb length is approximately constant.

In some aspects of the embodiment, the drying expiratory limb furtherincludes an insulating material attached to an outer surface of thewall. The insulating material can be configured to control thetemperature drop of the gas to increase drying of the gas along theexpiratory limb length. In some embodiments, an amount of the insulatingmaterial is substantially constant along the expiratory limb length. Theamount of the insulating material can vary along the expiratory limblength.

In some aspects, the drying expiratory limb can include a heater wireconfigured to selectively receive electrical power to provide heat tothe gas in the drying expiratory limb. In some aspects, the heater wireis configured to control the temperature drop of the gas to increasedrying of the gas along the expiratory limb length. In a further aspect,the drying expiratory limb includes two or more heaters that areconfigured to control the temperature of the gas to be above the dewpoint temperature by a targeted amount. In another aspect, the heaterwire has varying pitch spacing along the expiratory limb length, and, insome implementations, the pitch spacing increases with distance from thefirst end. In some implementations, the heater wire comprises at leasttwo sections, the two sections being configured to be independentlycontrolled using control circuitry.

In some aspects, a flow rate of the drying expiratory limb is configuredto improve breathability. For example, a cross-section of the dryingexpiratory limb can be increased to improve breathability.

In some aspects, the residence time is increased to improvebreathability. In some aspects, a profile of an absolute humidity of thegas is substantially parallel to a profile of a dew point temperature ofthe gas. In some aspects, the drying expiratory limb is configured tosubstantially eliminate rain out at the first end of the limb and at thesecond end of the limb. In some aspects, the drying expiratory limb isconfigured to substantially eliminate rain out at a ventilatorpositioned at the second end of the limb.

Some embodiments provide for a drying expiratory limb for use in arespiratory circuit. The drying expiratory limb includes a wall having afirst end and a second end separated by an expiratory limb length, thewall defining a space within and wherein at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thedrying expiratory limb includes a first opening in the first end of thewall, the first opening configured to receive a gas at a firsttemperature and a first relative humidity. The drying expiratory limbincludes a second opening in the second end of the wall configured toallow the gas to exit the drying expiratory limb, the gas having asecond temperature and a second relative humidity upon exiting thedrying expiratory limb. The drying expiratory limb is configured suchthat the first relative humidity and the second relative humidity areapproximately equal and a relative humidity of the gas at any pointalong the drying expiratory limb is approximately equal to the firstrelative humidity.

In some aspects, the relative humidity of the gas is at least about 95%,or at least about 99%. In some aspects, a decrease in temperature alongthe expiratory limb length is controlled according to a drying rate tokeep the relative humidity at a targeted humidity value, where thetargeted humidity value is between about 90% and about 99%, betweenabout 95% and about 99%, or between about 95% and about 97%.

Some embodiments provide for a drying expiratory limb of a breathingcircuit, the drying expiratory limb including a wall having a first endand a second end separated by an expiratory limb length, the walldefining a space within and wherein at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thedrying expiratory limb can include a first opening in the first end ofthe wall, the first opening configured to receive a gas at a firsttemperature and a first relative humidity. The drying expiratory limbcan include a second opening in the second end of the wall configured toallow the gas to exit the drying expiratory limb, the gas having asecond temperature and a second relative humidity upon exiting thedrying expiratory limb. The drying expiratory limb can be configuredsuch that a temperature of the gas remains above a dew point temperatureof the gas along the drying expiratory limb length. In some aspects, thedrying expiratory limb is configured such that a difference intemperature of the gas and the dew point temperature of the gas alongthe drying expiratory limb length is approximately constant.

In some aspects, the drying expiratory limb also includes an insulatingmaterial on an outer surface of the wall. In a further aspect, theinsulating material is configured to control the temperature of the gasto be between about 0.9° C. and 1° C. above the dew point temperature.In another aspect, an amount of the insulating material is substantiallyconstant along the expiratory limb length. In another aspect, an amountof the insulating material varies along the expiratory limb length.

In some aspects, a rate of temperature decrease from the first end to adistance of about 300 mm from the first end is less than or equal toabout 0.01° C./mm.

In some aspects, the drying expiratory limb further includes a heaterwire configured to selectively receive electrical power to provide heatto the gas in the drying expiratory limb. In a further aspect, theheater wire is configured to control the temperature of the gas to bebetween about 0.9° C. and 1° C. above the dew point temperature. Inanother aspect, the drying expiratory limb further includes a secondheater that is configured to control the rate of temperature decrease ofthe gas. In another aspect, the heater wire has varying pitch spacingalong the expiratory limb length. In a further aspect, the pitch spacingincreases with distance from the first end. In another aspect, theheater wire comprises at least two sections, the two sections beingconfigured to be independently controlled using control circuitry.

In some aspects, a residence time of the drying expiratory limb isconfigured to improve breathability. In a further aspect, a residencetime of the drying expiratory limb is decreased to improvebreathability.

In some aspects, a profile of an absolute humidity of the gas issubstantially parallel to a profile of the dew point temperature of thegas.

In some aspects, the drying expiratory limb is configured tosubstantially eliminate rain out at the first end of the wall and at thesecond end of the wall.

Some embodiments provide for a drying expiratory limb of a breathingcircuit and the drying expiratory limb includes a wall having a firstend and a second end separated by an expiratory limb length, the walldefining a space within and wherein at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thedrying expiratory limb includes a first opening in the first end of thewall, the first opening configured to receive a gas at a firsttemperature and a first relative humidity. The drying expiratory limbincludes a second opening in the second end of the wall configured toallow the gas to exit the drying expiratory limb, the gas having asecond temperature and a second relative humidity upon exiting thedrying expiratory limb. The drying expiratory limb is configured suchthat the first relative humidity and the second relative humidity areapproximately between about 90% and about 99%.

In some aspects, the first relative humidity of the gas or the secondrelative humidity of the gas or both are at least about 95%. In someaspects, the first relative humidity of the gas or the second relativehumidity of the gas or both are at least about 99%. In some aspects, adecrease in temperature along the expiratory limb length is controlledaccording to a drying rate to keep a relative humidity of the gas alongthe expiratory limb length within a targeted relative humidity range. Ina further aspect, the targeted relative humidity range is between about90% and about 99%.

Some embodiments provide for a drying expiratory limb of a breathingcircuit and the drying expiratory limb includes a wall having a firstend and a second end separated by an expiratory limb length, the walldefining a space within and wherein at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thedrying expiratory limb includes a first opening in the first end of thewall, the first opening configured to receive a gas at a firsttemperature and a first relative humidity. The drying expiratory limbincludes a second opening in the second end of the wall configured toallow the gas to exit the drying expiratory limb, the gas having asecond temperature and a second relative humidity upon exiting thedrying expiratory limb. The drying expiratory limb is configured suchthat a temperature of the gas remains approximately above a dew pointtemperature of the gas along the drying expiratory limb length, and arelative humidity of the gas remains approximately between about 90% and99%.

In some aspects, the drying expiratory limb is configured such that thetemperature of the gas remains approximately 1° C. above the dew pointtemperature of the gas along the drying expiratory limb length.

Some embodiments provide for a drying expiratory limb of a breathingcircuit and the drying expiratory limb includes a wall having a firstend and a second end separated by an expiratory limb length, the walldefining a space within and wherein at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thedrying expiratory limb includes a first opening in the first end of thewall, the first opening configured to receive a gas at a firsttemperature and a first relative humidity. The drying expiratory limbincludes a second opening in the second end of the wall configured toallow the gas to exit the drying expiratory limb, the gas having asecond temperature and a second relative humidity upon exiting thedrying expiratory limb. The drying expiratory limb is configured suchthat a temperature of the gas remains approximately 1° C. above a dewpoint temperature of the gas along the drying expiratory limb length.

Some embodiments provide for a limb having a multi-lumen design fordelivering humidified gas to or from a patient. Such a limb isparticularly useful for delivering and drying humidified gas from apatient. The limb includes a multi-lumen configuration, each lumenhaving a first end and a second end and a space within the lumen definedby a wall, and at least a part of said wall comprises a breathablematerial configured to allow transmission of water vapor butsubstantially prevent transmission of liquid water. The limb includes agas entry port configured to receive a gas at an entry temperature andan entry relative humidity for transmission along the limb. The limbincludes a gas exit port configured to allow the gas to exit the limb,the gas having an exit temperature and an exit relative humidity uponexiting the limb. The limb can be configured to increase a drying of thegas as it passes through the limb as compared to an expiratory limbcomprising a single lumen of a similar size and a similar material. Thelimb can be configured such that a difference between a temperature ofthe gas and a dew point temperature of the gas along the limb length isapproximately constant.

In some aspects, the multi-lumen configuration comprises a plurality ofconduits. In a further aspect, the plurality of conduits is configuredto increase residence time of gas in the limb at constant volumetricflow rate.

In some aspects, the limb further includes a heater wire configured toprovide heat to the gas passing through the expiratory limb. In someaspects, the heater wire is configured to deliver a greater amount ofheat to the gas near the entry port of the limb than to the gas near theexit port.

Some embodiments provide for a limb having a multi-lumen design fordelivering humidified gas to or from a patient in a medical circuit. Asdiscussed above, such a limb is particularly useful for delivering anddrying humidified gas from a patient. The limb includes a multi-lumenconfiguration, each lumen having a first end and a second end and aspace within the lumen defined by a wall, and at least a part of saidwall comprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thelimb includes a gas entry port configured to receive a gas at an entrytemperature and an entry relative humidity for transmission along thelimb. The limb includes a gas exit port configured to allow the gas toexit the limb, the gas having an exit temperature and an exit relativehumidity upon exiting the limb.

In some embodiments, the limb is configured to increase a drying of thegas as it passes through the limb as compared to an expiratory limbcomprising a single lumen of a similar size and a similar material. Thelimb can be configured such that the first relative humidity and thesecond relative humidity are approximately equal and a relative humidityof the gas at any point along the limb is approximately equal to thefirst relative humidity.

Some embodiments provide for a limb of a medical circuit and the limbincludes a multi-lumen configuration, wherein each lumen has a first endand a second end and a space within the lumen defined by a wall, atleast a part of said wall comprises a breathable material configured toallow transmission of water vapor but substantially prevent transmissionof liquid water. The limb includes a gas entry port configured toreceive a gas at an entry temperature and an entry relative humidity fortransmission along the expiratory limb. The limb includes a gas exitport configured to allow the gas to exit the expiratory limb, the gashaving an exit temperature and an exit relative humidity upon exitingthe expiratory limb. The multi-lumen design can be configured toincrease a drying of the gas as it passes through the expiratory limb ascompared to an expiratory limb comprising a single lumen of a similarsize and a similar material. The limb can be configured such that atemperature of the gas remains above a dew point temperature of the gasalong the limb length.

In some aspects, the multi-lumen configuration comprises a plurality ofconduits. In a further aspect, the plurality of conduits is configuredto decrease a flow rate in each lumen.

In some aspects, the limb further includes a heater wire configured toprovide heat to the gas passing through the expiratory limb. In afurther aspect, the heater wire is configured to deliver a greateramount of heat to the gas near the entry port of the expiratory limbthan to the gas near the exit port.

In some aspects, the number of lumens is less than or equal to 5. In afurther aspect, the number of lumens is equal to 3.

Some embodiments provide for a limb of a medical circuit and the limbincludes a multi-lumen configuration, wherein each lumen has a first endand a second end and a space within the lumen defined by a wall, atleast a part of said wall comprises a breathable material configured toallow transmission of water vapor but substantially prevent transmissionof liquid water. The limb includes a gas entry port configured toreceive a gas at an entry temperature and an entry relative humidity fortransmission along the expiratory limb. The limb includes a gas exitport configured to allow the gas to exit the expiratory limb, the gashaving an exit temperature and an exit relative humidity upon exitingthe expiratory limb. The multi-lumen design is configured to increase adrying of the gas as it passes through the expiratory limb as comparedto an expiratory limb comprising a single lumen of a similar size and asimilar material. The limb is configured such that the first relativehumidity and the second relative humidity are approximately betweenabout 90% and about 99%. In some aspects, the number of lumens is lessthan or equal to 5.

Some embodiments provide for a limb for use in a respiratory circuit andthe limb includes a multi-lumen configuration comprising less than sixlumens, wherein each lumen has a first end and a second end and a spacewithin the lumen defined by a wall, at least a part of said wallcomprises a breathable material configured to allow transmission ofwater vapor but substantially prevent transmission of liquid water. Thelimb includes a gas entry port configured to receive a gas at an entrytemperature and an entry relative humidity for transmission along theexpiratory limb. The limb includes a gas exit port configured to allowthe gas to exit the expiratory limb, the gas having an exit temperatureand an exit relative humidity upon exiting the expiratory limb. Themulti-lumen design is configured to increase a drying of the gas as itpasses through the expiratory limb as compared to an expiratory limbcomprising a single lumen of a similar size and a similar material.

In at least one embodiment, a limb is provided that is suitable for usein a medical circuit, the limb comprising a first opening configured toreceive a gas at a first temperature and a first relative humidity; asecond opening configured to allow the gas to exit the limb, the gashaving a second temperature and a second relative humidity; and aplurality of conduits each comprising a first end proximal the firstopening, a second end proximal the second opening, and a wall extendingbetween the end and the second end and defining a lumen within throughwhich, when in use, gas flows in the direction of the first end towardthe second end, and wherein at least a part of said wall comprises abreathable material configured to allow transmission of water vapor butsubstantially prevent transmission of liquid water.

In various embodiments, the foregoing limb has one, some, or all of thefollowing properties, as well as properties described elsewhere in thisdisclosure. The breathable material can be foam. The material can have asubstantially uniform thickness. The limb can comprise three conduits.The plurality of conduits can be corrugated. The void fraction of thefoam material can be greater than 40%. The pneumatic compliance of thelimb can be less than 10 mL/kPa/m. The void fraction of the foammaterial can be about 45%. The pneumatic compliance of the limb can beless than 3 mL/kPa/m. The plurality of conduits can be twisted orbraided between the first opening and the second opening. The limb canfurther comprise one or more securing mechanisms configured to hold theplurality of conduits together. Each securing mechanism can comprise aplurality of lobes, and each of the conduits can pass through one of thelobes. Each securing mechanism can be a trefoil comprising a pluralityof rings, and each of the conduits can pass through one of the rings.The limb can further comprise a connector comprising a unitary portioncomprising an aperture defining the first opening or the second opening,a multipartite portion comprising a plurality of passages, eachconfigured to connect to one of the plurality of conduits, and aninternal ogive comprising a base attached to or formed on themultipartite portion between the plurality of passages, the ogiveextending in the direction of the unitary portion and configured todirect the flow of gas from the multipartite portion to the unitaryportion or from the unitary portion to the multipartite portion. Thelimb can further comprise at least one heater wire configured to provideheat to the gas passing through the limb. The wall of at least one ofthe conduits can encompass or have embedded thereon a heater wireconfigured to provide heat to the gas passing through the lumen. Thelumen of at least one of the conduits can encompass a heater wireconfigured to provide heat to the gas passing through the lumen. Thelimb can be an expiratory limb and the first opening can be configuredto receive gas from a patient interface.

In at least one embodiment, a device suitable for use with a limb of amedical circuit, comprises a unitary portion comprising an apertureconfigured to connect to a patient interface or a humidification device,a multipartite portion comprising a plurality of passages, eachconfigured to connect to one of the plurality of conduits, and aninternal ogive comprising a base attached to or formed on themultipartite portion between the plurality of passages, the ogiveextending in the direction of the unitary portion and configured todirect the flow of gas from the multipartite portion to the unitaryportion or from the unitary portion to the multipartite portion.

In various embodiments, the foregoing device has one, some, or all ofthe following properties, as well as properties described elsewhere inthis disclosure. The multipartite portion can comprise three passages.

In at least one embodiment, a limb suitable for use in a medical circuitcomprises a first opening configured to receive a gas at a firsttemperature and a first relative humidity; a second opening configuredto allow the gas to exit the limb, the gas having a second temperatureand a second relative humidity; and means for increasing the residencetime of gas flow within the limb between the first opening and thesecond opening.

In various embodiments, the foregoing limb has one, some, or all of thefollowing properties, as well as properties described elsewhere in thisdisclosure. The residence-time-increasing means can comprise a pluralityof conduits between the first opening and the second opening, each ofthe conduits comprising a wall extending between the first opening andthe second opening and defining a lumen within through which, when inuse, gas flows in the direction of the first opening toward the secondopening. At least a part of the wall can comprise a breathable foammaterial configured to allow transmission of water vapor butsubstantially prevent transmission of liquid water.

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers may be reused to indicategeneral correspondence between reference elements. The drawings areprovided to illustrate example embodiments described herein and are notintended to limit the scope of the disclosure.

FIG. 1 illustrates an example respiratory system for deliveringhumidified gas to a user, the respiratory humidification system having abreathing circuit that includes a drying expiratory limb configured tohave a linear temperature profile as a function of distance along thedrying expiratory limb.

FIG. 2 illustrates a plot of a temperature of a gas as a function ofposition along an expiratory limb.

FIG. 3 illustrates a drying expiratory limb with varying insulation tocontrol the temperature of the gas along the limb.

FIG. 4 illustrates a drying expiratory limb with two sections thatinclude breathable insulation to control a temperature drop at abeginning of the limb and at an end of the limb.

FIG. 5 illustrates a drying expiratory limb having multiple heater wiresthat have a pitch spacing that is different in different sections.

FIG. 6 illustrates a drying expiratory limb having a coiled heater wirethat has a pitch spacing that is different in different sections.

FIG. 7 illustrates a drying expiratory limb having a straight heaterwire with zones of varying pitch spacing within the wire.

FIG. 8 illustrates a drying expiratory limb having multiple sectionswherein a system is configured to independently control the differentsections of heater wire.

FIG. 9 illustrates a drying expiratory limb having a heater wire that isfolded back upon itself at a patient end to control a temperature dropat a front end of the drying expiratory limb.

FIG. 10 illustrates a drying expiratory limb combining a varyinginsulation layer with a heater wire with a varying pitch.

FIGS. 11A-11B illustrate various multi-lumen configurations for a dryingexpiratory limb.

FIGS. 11C-11D illustrate drying expiratory limbs configured to increasea surface area using different cross-section shapes.

FIG. 12 illustrates a drying expiratory limb combining multiple lumensand varying insulation.

FIG. 13 illustrates a drying expiratory limb with a cross-sectionsimilar to the drying expiratory limbs illustrated in FIG. 11D and aheater wire with a varying pitch spacing along its length.

FIG. 14 illustrates a drying expiratory limb with a multi-lumen designin conjunction with heater wires in each lumen.

FIG. 15 illustrates various multi-lumen configurations for a limb forconveying humidified gas in a medical circuit.

FIG. 16 illustrates a securing mechanism for use with a multi-lumenlimb.

FIGS. 17A-17D illustrate a connector for use with one or both ends of amulti-lumen limb. FIG. 17E illustrates the connector in use on amulti-lumen limb.

DETAILED DESCRIPTION

Certain embodiments and examples of limbs for conveying humidified gasin medical circuits are described herein. Those of skill in the art willappreciate that the disclosure extends beyond the specifically disclosedembodiments and/or uses and obvious modifications and equivalentsthereof. Thus, it is intended that the scope of the disclosure not belimited by any particular embodiments described herein.

It is desirable to provide a breathable limb for use in a medicalcircuit. Breathable is used herein to mean appreciably permeable towater vapor and substantially impermeable to liquid water and the bulkflow of gases. Breathability can be desirable to reduce or prevent rainout. “Rain out,” or condensation, can be a problem when high humiditygases within a limb come into contact with the walls of a limb at alower temperature. However, rain out depends on many factors, includingnot only the temperature profile in the limb, but also the gas flowrate, component geometry, and the intrinsic breathability of thematerial used to form the component. In general, a breathable limb canbe desirable because it allows water from a high-humidity gas flowwithin a limb to pass into a low-humidity environment, ameliorating thepotential for rain out within the limb. Conversely, and depending uponthe application, breathability can also be desirable to allow water froma high-humidity environment to pass into and thereby humidify a gas flowwithin a limb.

Furthermore, it can also be advantageous to control the temperatureand/or relative humidity of the gas passing through the limb.Temperature and/or relative humidity control can limit or preventcondensation in a downstream/upstream device or interface, rain out inthe limb, to increase drying of the gas, or any combination of these.

Descriptions of limbs for conveying humidified gas in a medical circuitare presented herein that include breathable material configured to passwater vapor and to substantially prevent liquid water from passingthrough. Any suitable breathable material can be used. Nevertheless,particularly suitable breathable materials are described in PCTPublication WO 2011/077250, entitled “Components for Medical Circuits,”filed Dec. 22, 2010, which is hereby incorporated by reference in itsentirety and made a part of this specification. As described in thatpublication, the breathable material can be a breathable foamed materialconfigured to allow the transmission of water vapor but substantiallyprevent the transmission of liquid water. The breathable foamed materialcan comprise a blend of polymers. The breathable foamed material cancomprise a thermoplastic elastomer with a polyether soft segment. Thebreathable foamed material can comprise a copolyester thermoplasticelastomer with a polyether soft segment. The breathable foamed materialcan comprise a thermoplastic elastomer with a polyether soft segment.

As discussed in more detail below with reference at least to FIG. 1 ,expiratory limbs can be included in medical circuits. As used herein, anexpiratory limb is broadly defined to mean a limb that transmitshumidified gases from a patient in a medical circuit. Expiratory limbsare suitable for breathing circuits for use in respiratory applications.For an unheated expiratory limb, as the gas travels along the limbtowards a ventilator, ambient, or gas source, the gas will cool at arate that is higher than its drying rate. As a result, the temperatureof the gas can drop below the dew point temperature, causingcondensation to form inside the expiratory limb. For a heated expiratorylimb, the gas may be kept at a high temperature for too long. As the gasdries, the relative humidity of the gas can drop (as the temperature ofthe gas is relatively constant over a portion of the limb), whichimpairs further drying, as drying is more efficient when the relativehumidity is at or near about 100%. If the gas has not been dried enough,when the temperature drops in the ventilator then condensation can formin the ventilator.

Accordingly, it may be advantageous to improve or optimize drying alongthe length of the expiratory limb, which can be accomplished, in someembodiments, by maintaining the relative humidity at a substantiallyconstant value. In some embodiments, improved or optimized drying mayoccur where the relative humidity remains between about 90% and about99%, between about 95% and about 99%, or between about 95% and about97%. It may also be advantageous to reduce the temperature of the gasalong the length of the limb so that the temperature of the gas exitingthe expiratory limb is at or near the temperature of the ventilator, gassource, or ambient.

An effective method of doing this is to have the humidity and/ortemperature decrease in a tailored manner along the length of the limb.For example, it may be advantageous to tailor the rate of temperaturedecrease across the first portion of the expiratory limb so that it doesnot exceed about 0.01° C./mm, or so that the temperature drop is betweenabout 0° C./mm and about 0.009° C./mm. In some embodiments, it may beadvantageous to limit the rate of temperature decrease to the statedranges from the beginning of the limb to about the first 300 mm or 400mm of the expiratory limb. It may be advantageous to also limit thetotal temperature drop across the limb to be less than or equal to about10° C. and/or between about 3° C. and 10° C. In some embodiments, dryingwithin a limb is limited by the relative humidity. In some embodiments,it may be desirable to have the temperature drop in a linear or a nearlylinear fashion along the limb.

Therefore, the expiratory limbs described herein have been configured toachieve the goals of reducing or eliminating rain out or condensation inthe ventilator through controlling the environment within the limb. Forexample, for a gas with a relative humidity of about 95%, the expiratorylimb can be configured to tailor the temperature profile such that thedifference between the temperature of the gas and the dew pointtemperature is less than about 1.5° C., less than about 1° C., orbetween about 0.9° C. and about 1° C. The heating or insulation of thelimb can be configured to keep the temperature within a“non-condensation window” which can be a temperature range that liesbetween the dew point temperature line and the absolute humidity line sothat little or no condensation occurs within the expiratory limb or atthe ventilator.

In some embodiments, an example temperature profile that reducescondensation, reduces rain out, and that provides the advantageousproperties described herein can be where an initial temperature drop(e.g., from the patient interface) from the beginning of the limb toabout the first 300 or 400 mm can have a slope that is between about 0°C./mm and about 0.01° C./mm. In some embodiments, a temperature profilethat has a total drop in temperature between about 3° C. and about 10°C. may provide at least some of the advantages set forth herein.

Embodiments of expiratory limbs will be now described herein withreference to their use in a respiratory system. It is to be understood,however, that the limbs described herein can be used with a variety ofapplications where it is desirable to increase the residence time of agas flow from a first environment to a second environment havingdifferent temperatures and/or humidity, such as incubation systems,surgical humidification systems, and the like.

FIG. 1 illustrates an example respiratory system 100 for deliveringhumidified gas to a user, the humidification system 100 having abreathing circuit 200 that includes an inspiratory limb 202 and anexpiratory limb 210. The illustrated respiratory humidification system100 comprises a pressurized gas source 102. In some implementations, thepressurized gas source 102 comprises a fan, blower, or the like. In someimplementations, the pressurized gas source 102 comprises a ventilatoror other positive pressure generating device. The pressurized gas source102 comprises an inlet 104 and an outlet 106.

The pressurized gas source 102 provides a flow of fluid (e.g., oxygen,anesthetic gases, air or the like) to a humidification unit 108. Thefluid flow passes from the outlet 106 of the pressurized gas source 102to an inlet 110 of the humidification unit 108. In the illustratedconfiguration, the humidification unit 108 is shown separate of thepressurized gas source 102 with the inlet 110 of the humidification unit108 connected to the outlet 106 of the pressurized gas source 102 with aconduit 112. In some implementations, the pressurized gas source 102 andthe humidification unit 108 can be integrated into a single housing.

The gases flow through the inspiratory limb 202 to the patient 101through a patient interface 115. The expiratory limb 210 also connectsto the patient interface 115. The expiratory limb 210 is configured tomove exhaled humidified gases away from the patient 101. Here, theexpiratory limb 210 returns exhaled humidified gases from the patientinterface 115 to the gases source 102. Alternatively, exhaled humidifiedgases can be passed directly to ambient surroundings or to otherancillary equipment, such as an air scrubber/filter (not shown). Anysuitable patient interface 115 can be incorporated. Patient interface isa broad term and is to be given its ordinary and customary meaning to aperson of ordinary skill in the art (that is, it is not to be limited toa special or customized meaning) and includes, without limitation, masks(such as face masks and nasal masks), cannulas, and nasal pillows. Apatient interface usually defines a gases space which, when in use,receives warm humid breathing gases.

While other types of humidification units can be used with certainfeatures, aspects, and advantages described in the present disclosure,the illustrated humidification unit 108 is a pass-over humidifier thatcomprises a humidification chamber 114 and an inlet 110 to thehumidification chamber 114. In some implementations, the humidificationchamber 114 comprises a body 116 having a base 118 attached thereto. Acompartment can be defined within the humidification chamber 116 that isadapted to hold a volume of liquid that can be heated by heat conductedor provided through the base 118. In some implementations, the base 118is adapted to contact a heater plate 120. The heater plate 120 can becontrolled through a controller 122 or other suitable component suchthat the heat transferred into the liquid can be varied.

The controller 122 of the humidification unit 108 can control operationof various components of the respiratory humidification system 100.While the system as illustrated uses a single controller 122, multiplecontrollers can be used in other configurations. The multiplecontrollers can communicate or can provide separate functions and,therefore, the controllers need not communicate. In someimplementations, the controller 122 may comprise a microprocessor, aprocessor, or logic circuitry with associated memory or storage thatcontains software code for a computer program. In such implementations,the controller 122 can control operation of the respiratoryhumidification system 100 in accordance with instructions, such ascontained within the computer program, and also in response to internalor external inputs.

The body 116 of the humidification chamber 114 comprises a port 124 thatdefines the inlet 110, and a port 126 that defines an outlet 128 of thehumidification chamber 114. As liquid contained within thehumidification chamber 114 is heated, liquid vapor is mixed with gasesintroduced into the humidification chamber 114 through the inlet port124. The mixture of gases and vapor exits the humidification chamber 114through the outlet port 126.

The humidification system 100 includes a breathing circuit 200comprising the inspiratory limb 202 connected to the outlet 128 thatdefines the outlet port 126 of the humidification unit 108. Theinspiratory limb 202 conveys toward a user the mixture of gases andwater vapor that exits the humidification chamber 114. The inspiratorylimb 202 can include a heating element 206 positioned along theinspiratory limb 202, wherein the heating element 206 is configured toreduce condensation along the inspiratory limb 202, to control atemperature of gas arriving at the user, or both. The heating element206 can raise or maintain the temperature of the gases and water vapormixture being conveyed by the inspiratory limb 202. In someimplementations, the heating element 206 can be a wire that defines aresistance heater. By increasing or maintaining the temperature of thegases and water vapor mixture leaving the humidification chamber 114,the water vapor is less likely to condense out of the mixture.

Expiratory Limb

The humidification system 100 includes an expiratory limb 210 configuredto carry away expired gas from the user and deliver it to the gas source102. The expiratory limb 210 can include a wall having a first end atthe patient end to receive the expired or exhaled gas and a second endat the gas source 102, the two ends being separated by an expiratorylimb length. The wall can define a space for the gas to travel (e.g.,one or more lumens) and at least a portion of the wall can include abreathable material.

If the gas cools too quickly along the expiratory limb 210, the gas canbecome supersaturated as the water vapor cannot pass through thebreathable layer quickly enough. This can cause, at least in part, rainout near the patient end of the expiratory limb 210. If the gas coolstoo slowly, rain out can form near the second end of the expiratory limb210, where the relatively hot gas comes into contact with cooler air atthe gas source 102 or ambient. To reduce or prevent rain out in theexpiratory limb, characteristics of the gas or the expiratory limb 210can be controlled. For example, by controlling the temperature profileof the gas and other variables in the expiratory limb 210, thebreathability of the expiratory limb 210 can be improved. In someembodiments, the breathability of the expiratory limb 210 can increaseby increasing transit time through the expiratory limb 210, which can beaccomplished, in some embodiments, by decreasing a flow rate or byincreasing a length of the passage through expiratory limb 210.Increasing the transit time through the expiratory limb may, in someimplementations, increase heat loss of the gas through the expiratorywall. If this occurs too quickly, as stated above, rain out can occur.In some embodiments, providing a substantially linear temperatureprofile along the expiratory limb 210 and/or increasing a transit timethrough the expiratory limb 210 can increase the breathability of theexpiratory wall by about 40% to about 70% or more. Accordingly, in someembodiments, the expiratory limb 210 can be configured to have asubstantially linear temperature profile such that the temperature ofthe gas drops in a linear fashion across the length of the expiratorylimb 210. Relatedly, in some embodiments, the expiratory limb 210 can beconfigured to keep a difference between the gas temperature and its dewpoint temperature substantially constant across the length of theexpiratory limb 210. Similarly, in some embodiments, the expiratory limb210 can be configured to keep a relative humidity of the gas at betweenabout 95% to about 99% across the length of the expiratory limb 210.

In some embodiments, the expiratory limb 210 includes insulationconfigured to control a temperature profile in the expiratory limb. Insome embodiments, the expiratory limb 210 includes an associated heatingelement 212 that is arranged along the expiratory limb 210, wherein theheating element 212 is configured to maintain a substantially lineartemperature drop along the expiratory limb 202, to control a relativehumidity of the gas, to control a temperature of the gas relative to itsdew point temperature, or any combination of these.

The heating element 212 can be selectively controlled by the controller122 in the humidification system 100 or through other means. Thecontroller 122 can be configured to control the heating element 210, toreceive feedback from sensors in the system, to provide logic to controlpower to the heating element 212, to adjust control of the heatingelement 212 in response to temperature readings from sensors, and thelike. In some embodiments, the controller 122 includes a power sourceconfigured to deliver electrical power to the heating element 212. Thecontroller 122, for example, can control an amount of heat delivered bythe heating element 212 by delivering a variable power, a variablecurrent, a variable voltage, or any combination of these to the heatingelement 212. The controller 122 can implement pulse-width-modulation tocontrol the heating element 212. The controller 122 can apply asubstantially constant electrical power until a desired temperature isreached within the expiratory limb 210. In some embodiments, theexpiratory limb 210 includes one or more sensors configured to providethe controller or a user with information regarding the characteristicsof the gas in the expiratory limb 210 which can include, for example,temperature, relative humidity, absolute humidity, or any combination ofthese and this information can be provided at one or more points alongthe expiratory limb 210. In some implementations, the heating element206 can be a wire that defines a resistance heater.

In some embodiments, the expiratory limb 210 can include insulation incombination with the heating element 212. In some embodiments, theheating element 210 can be configured to provide zone heatingcapabilities such that different portions of the expiratory limb 210receive different amounts of heat. This can be accomplished, forexample, by using multiple heating wires or a single wire with differentwinding densities or pitch spacing at different points.

Example Expiratory Limbs with Tailored Temperature Profiles

FIG. 2 illustrates a plot of a temperature of a gas as a function ofposition along an expiratory limb. The two plots listed as “Control” andshown with dashed lines illustrate some expiratory limbs that have beenconfigured to dry gases using breathable materials. The four plotslisted as “Improved Drying” and shown with solid lines illustrateresults when using some embodiments described herein. They represent animproved or optimized drying of the gases through the expiratory limbs.The six plots listed as “Condensation” and shown with dotted linesrepresent expiratory limbs with temperature profiles that experiencerain out or condensation within the limb or at the ventilator. Theseexpiratory limbs experience a rate of temperature decrease from thebeginning of the expiratory limb to about 300 mm or 400 mm that exceedsabout 0.009° C./mm or about 0.01° C./mm and/or where the totaltemperature drop exceeds about 10° C. or is between about 3° C. andabout 10° C.

Table 1 lists information related to the absolute humidity and dew pointtemperature for the temperature profiles of the two “Control” plots andthe 4 “Improved Drying” plots in FIG. 2 . The table lists the inputabsolute humidity (“AH In”) and the output absolute humidity (“AH Out”)and the dew point temperature (“DPT”) of the exit gas.

TABLE 1 Absolute humidity and dew point temperature of exampleexpiratory limbs Sample AH In [mg/L] AH Out [mg/L] DPT [° C.] Control 144.1 35.0 32.7 Control 2 43.4 28.3 28.7 Improved 1 43.4 25.1 26.5Improved 2 45.3 26.5 27.5 Improved 3 42.3 26.3 27.4 Improved 4 43.2 24.926.4Example Expiratory Limbs

Example configurations of expiratory limbs will now be described. Thevarious embodiments described herein and illustrated in the figures areintended to be illustrative of various implementations that achieve astated goal of reducing condensation in a ventilator and/or rain out inthe expiratory limb. Many different variations and permutations arepossible which do not depart from the scope of the examples providedherein. Thus, it is to be understood that the following examples shouldnot be interpreted as limiting the scope of the disclosure, and thescope of the present disclosure extends beyond these enumeratedexamples.

Generally, the example expiratory limb designs can be configured toaddress situations where radiation of energy from the expiratory limb toambient or the external atmosphere can cause too rapid a temperaturedrop at the entrance to the expiratory limb, which can causecondensation in this section of the limb. This situation can be commonwhen the external temperature is relatively low, flow rate is relativelylow and/or external relative humidity is relatively high (factors whichcan reduce breathability of the expiratory limb). Under such conditionsit may be advantageous to decrease the rate of temperature change.

Relatedly, if conditions are present that limit or reduce thebreathability of the expiratory limb, then it may be advantageous tohave a relatively high exit temperature to limit condensation at theexit of the limb (e.g., upon entering the ventilator or gas source). Forexample, where the external relative humidity is relatively high or whenthe flow rate is relatively high, the breathability of the expiratorylimb may be reduced.

Thus, example expiratory limbs are included and described herein thatcan be configured to deal with a wide range of conditions that may causecondensation. These designs could be modified where it is more desirableto address one condition over another or to enhance or improve efficacyrelated to a particular problem. The expiratory limbs presented hereincan be configured to address situations where external temperature isrelatively low, flow rate is relatively low, or external relativehumidity is relatively high.

FIG. 3 illustrates an expiratory limb 210 with varying insulation 214 tocontrol the temperature of the gas along the limb. The single conduithas several different sections having different insulation values. Theinsulation values are represented in FIG. 3 as different sizes ofinsulating material 214. However, the physical sizes of the insulatingelements 214 do not have to decrease along the length and the sizes canbe substantially identical along the length. To increase the effect ofinsulating elements 214, a thickness of the insulating material 214 canbe increased, a density of the insulating material 214 can be increased,different materials can be used, etc. The insulating values can beconfigured to provide a relatively linear or slightly concavetemperature profile over a range of temperature conditions, relativehumidity, and/or flow rates. In some embodiments, the insulationsections along the limb are not discrete, but can be substantiallycontinuous, or it can be configured to have insulation sections thatchange in a substantially continuous manner combined with sections thatprovide a discrete change in insulation value. The number of insulatingsections can be any suitable number including, for example, 2, 3, 4, 5,6, 7, 8, 10, 15, 20, 50, or more.

FIG. 4 illustrates an expiratory limb 210 with two sections that includebreathable insulation 214 to control a temperature drop at a beginningof the limb and at an end of the limb. This configuration may beadvantageous because the insulation material 214 is used where gas tendsto experience relatively rapid cooling. The insulation values, extent ofinsulation, and placement of the insulation 214 can be configured toprovide the advantages described herein. Additional insulating sectionsmay be included as well.

FIG. 5 illustrates a expiratory limb 210 having multiple heater wires212 that have a pitch spacing that is different in different sections ora single heater wire 212 with varying pitch spacing or a combination ofboth. This represents an active temperature control mechanism. As such,the heater wire or wires 212 can be coupled to the controller 122, asdescribed herein with reference to FIG. 1 , with the attendant controlmechanisms described there. Similarly, the heater wires illustrated inFIGS. 4-9 can be controlled using the heater wire.

The heater wires 212 can be configured to be outside the tubing and canhave different spacing along the limb. Near the patient end, the spacingcan be relatively close together to generate or apply more heat comparedto the heat applied closer to the limb exit. In some embodiments, therecan be different zones with different winding densities to achieve anear linear temperature profile. In some embodiments, the number ofsections with different spacing can be 2, 3, 4, 5, 6, 7, 8, 10, 15, 20,25, 50, or more or the spacing of the windings can increasesubstantially smoothly with distance from the patient end. In someembodiments, the heater wire 212 comprises multiple, individual heatingelements which can be collectively and/or individually controlled.

FIG. 6 illustrates an expiratory limb 210 having a coiled heater wire212 that has a pitch spacing that is different in different sections.The heater wire 212 can be positioned within the limb. The windingconfiguration can be similar to the configurations described herein withreference to FIG. 5 . In some embodiments, the heater wire 212 comprisesmultiple, individual heating elements which can be collectively and/orindividually controlled.

FIG. 7 illustrates an expiratory limb 210 having a straight heater wirewith zones of varying pitch spacing within the wire. The pitch spacingcan be configured similar to the winding density and spacing describedherein with reference to FIGS. 5 and 6 . In some embodiments, the heaterwire 212 comprises multiple, individual heating elements which can becollectively and/or individually controlled.

FIG. 8 illustrates an expiratory limb 210 having multiple heatersections wherein a system is configured to independently control thedifferent sections of heater wire 212. As shown, the heater is dividedinto sections which can be selectively controlled by the controller 122through the connectors 216 a and 216 b. There can be more sections withaccompanying connectors, and the description here is limited to threesections with two connectors.

Connectors 216 a and 216 b couple the first and second heater segmentsand allow the controller to selectively apply heat to different sectionsof the expiratory limb 210. The connectors 216 a, 216 b can beconfigured to electrically couple the heater wires 212 in the segmentsto enable control of the heater wires 212 using the controller 122. Theconnector 216 a, 216 b can be configured to electrically coupletemperature sensors (not shown) to enable the controller 122 to acquiretheir respective outputs. The connectors 216 a, 216 b can includeelectrical components that enable selective control of the heater wires212. For example, the connectors 216 a, 216 b can include electricalcomponents that direct power through the heater wires 212 in a firstsection in a first operation mode and through the heater wires 212 inboth the first section and a second section in a second operation mode.The electrical components included on the connector 216 a, 216 b caninclude, for example and without limitation, resistors, diodes,transistors, relays, rectifiers, switches, capacitors, inductors,integrated circuits, micro-controllers, micro-processors, and the like.In some embodiments, the connector 216 a, 216 b can be configured to beinternal to the expiratory limb 210 such that it is substantiallyshielded from external elements. In some embodiments, some of theelectrical components on the connector 216 a, 216 b can be configured tobe physically isolated from the humidified gas within the expiratorylimb 210 to reduce or prevent damage that may result from exposure tohumidity. In some embodiments, the connector 216 a, 216 b can includerelatively inexpensive passive electrical components to reduce costand/or increase reliability.

FIG. 9 illustrates an expiratory limb 210 having a heater wire 212 thatis folded back upon itself at a patient end to control a temperaturedrop at a front end of the expiratory limb 210. The extent of thefolding can be configured to provide a desired or advantageoustemperature profile near the patient end of the limb 210. For example,it may be advantageous to limit the initial temperature drop to reducecondensation at the patient inlet so providing additional heat at thislocation may reduce or prevent rain out near the inlet.

FIG. 10 illustrates an expiratory limb 210 combining a varyinginsulation layer 214 with a heater wire 212 with a varying pitch. Thisembodiment is similar to combining the elements from FIG. 3 and FIG. 6 .The sections of relatively constant insulation value and relativelyconstant winding density need not coincide. Transitions betweeninsulation values and/or winding densities can be varied and can beindependent from one another. This embodiment also illustrates thatpassive and active control approaches may be utilized in the expiratorylimb 210.

Limbs with Non-Cylindrical Lumens and/or Multiple Lumens

FIGS. 11 through 15 illustrate some embodiments of limbs employingnon-cylindrical or multi-lumen designs. As used herein, a multi-lumenlimb is broadly defined to mean a limb having more than one lumen, suchthat the gas flow through one lumen is separated from the gas flowthrough any other lumen by at least one wall. Non-limiting embodimentsof multi-lumen designs are shown in FIGS. 11A, 11B, 12, 14, and 15 . Asused herein, a non-cylindrical limb is broadly defined to mean a limbhaving a lumen that is not shaped like a cylinder. Non-limitingembodiments of non-cylindrical designs are shown in FIGS. 11C, 11D, and13 . Certain embodiments can comprise a combination of such elements.For example, a limb can have a multi-lumen design comprising one or morenon-cylindrical lumens.

In some embodiments, a multi-lumen limb comprises multiple conduitstwisted or braided together. This may advantageously provide for reducedflow volume in the limb for the gas because the gas flow in each lumenis one third of the gas flow in a comparable single-lumen limb. Thelower flow volume can increase the opportunity for evaporation from thewall surrounding the lumen. This configuration can also advantageouslyprovide for an increased residence time in the limb for the gas becausethe length of the individual conduits is longer due at least in part tothe twisting or braiding, while the overall length of the limb is ashorter standard commercial length. The increased residence time canincrease the breathability of the limb at constant volumetric flow rate,as it increases the opportunity for evaporation from the wallsurrounding the lumen.

Although the limb is described below with reference to an expiratorylimb 210, it should be understood that such a limb is suitable for usein a variety of environments for transporting humidified air to or froma patient that would benefit from an increased residence time.

FIGS. 11A-11B illustrate various multi-lumen configurations. Themulti-lumen limb 210 can include two or more individual conduits 211joined together in various ways and in various geometricalconfigurations. In some embodiments, the conduits 211 are physicallyseparated from one another to allow an increase in breathability throughthe conduit walls. In some embodiments, the limb 210 can includeinsulation material 214 surrounding the bundled conduits 211, asillustrated in FIG. 11B. Several geometrical configurations areillustrated in FIGS. 11A and 11B, but other configurations are possibleas well. For example, FIGS. 11C-11D illustrate limbs 210 that do notcomprise multiple individual conduits but which are configured toincrease residence time using different cross-section shapes. FIG. 11D,in particular, illustrates that many different cross-section shapes arepossible including regular or irregular shapes. In addition, any of theforegoing multi-lumen embodiments may include insulation material 214,as illustrated in FIG. 11D. In some embodiments, the shape of theconduit or conduits 211 can change along the length of the limb. Forexample, the conduit 211 can have a generally circular shape near thepatient end which can change to a triangle at a point along the length,which can then change to a star shape or shape similar to any of theembodiments in FIG. 11C or 11D. This can change the surface area overthe length of the limb, affecting the breathability and, hence, thetemperature profile.

FIG. 12 illustrates a limb 210 combining multiple conduits 211 andvarying insulation 214. This limb 210 represents a passive temperaturecontrol approach to the multi-lumen design. In some embodiments, usingthe multi-lumen design can increase the breathability of the limb 210.Using the insulation material 214 can decrease a rate of cooling thatmay increase where breathability increases. The insulation material canbe configured to reduce cooling while not adversely affecting thebreathability of the expiratory limb 210.

The individual conduits of a multi-lumen limb are desirably formed of abreathable material. In at least one embodiment, the individual conduitsof a multi-lumen limb 210 are formed of corrugated foam as described inPCT Publication WO 2011/077250 and/or as commercially embodied in Evaqua2™ conduits. Another suitable material is a breathable polyesterthermoplastic elastomer having a porosity of about 14%. Such material iscommercially embodied in Evaqua™ conduits. In at least one embodiment,each conduit of the multi-lumen limb is corrugated. The corrugatedconduit can have a maximum outside diameter (at the corrugation peak) of14.45 mm (or about 14.45 mm) or 15.15 mm (or about 15.15 mm). Thecorrugated conduit can have a minimum outside diameter (at thecorrugation valley) of 12.7 mm (or about 12.7 mm). The period of thecorrugation profile (the peak-to-peak distance) can be 3.14 mm (or about3.14 mm). The amplitude of the corrugation (peak-to-valley distance) canbe 1.7525 mm (or about 1.7525 mm). The wall thickness can be in therange of 0.5 mm and 1.0 mm (or in the range of about 0.5 mm and about1.0 mm), and more particularly in the range of 0.6 mm and 0.9 mm (or inthe range of about 0.6 mm and about 0.9 mm). For example, the wallthickness proximal corrugation peaks can be in the range of 0.50 mm and0.65 mm (or in the range of about 0.5 mm and about 0.65 mm). As afurther example, the wall thickness proximal corrugation valleys can bein the range of 0.80 mm and 1.0 mm (or about 0.80 mm and about 1.0 mm).

The conduit(s) can comprise reinforcing ribs, if desired. Such ribs areshown and described in conjunction with at least FIGS. 7A, 7B, 8A, and8B of PCT Publication WO 2011/077250. Such ribs are also commerciallyembodied in Evaqua 2™ conduits. As described in the publication, theseribs are used to reinforce the foam and, among other things, lower thepneumatic compliance of the limb to acceptable values (less than 10mL/kPa/m).

It was realized that the multi-lumen configuration can beself-reinforcing, which can reduce or eliminate a need for additionalreinforcing structures such as internal or external ribs disposed on theconduit walls. Thus, the ribs can be eliminated in certain embodiments.

Eliminating the reinforcing ribs can be desirable because it can improvebreathability. As shown in FIGS. 7A, 7B, 8A, and 8B of PCT PublicationWO 2011/077250, the conduit wall thickness at the ribs is substantiallygreater than the conduit wall thickness between the ribs. The ribstherefore reduce the overall active (breathable) area of the limb. Amulti-lumen construction without ribs according to this disclosure canhave 15% (or about 15%) greater active area than an Evaqua 2™ conduit.

Table 2 compares the breathability of a multi-lumen limb comprisingthree individual conduits with various single-lumen limbs. All of theconduits/limbs are formed of the same foam material, as described in PCTPublication WO 2011/077250. The adult Evaqua 2™ limbs have reinforcingribs, and the foam material has a void fraction of 0.35. The individualconduits of the multi-lumen limb do not have reinforcing ribs, and thefoam material has a void fraction of 0.448. Limb A is an adult Evaqua 2™limb with the gas stream heated with a heater cable. Limbs B and C areadult Evaqua 2™ limbs with the gas stream unheated. Limb D is themulti-lumen limb with the gas stream unheated. All experiments wereconducted with a gas flow rate of 20 L/min through the sample limb, anominal external temperature of 18-19° C. The runtime for the experimentwas 6.5 hours with a total gas flow of 7,800 L. The inlet gas wasestimated to be 36° C. at 98% relative humidity (RH). The resultsmeasured were the exit gas temperature, the dew point of the exit gas,the amount of water condensate outside the limb and the amount of watercondensate in the limb at the end of the experiment.

TABLE 2 BREATHABILITY PERFORMANCE Limb Limb Limb Limb A B C D Flow,L/min 20 20 20 20 Outside Condensate, g 2.2 5.8 6.7 0.9 InsideCondensate, g 0 22.0 22.8 0.0 Total Condensate, g 2.2 27.8 29.5 0.9Temperature exit gas, ° C. 39.2 27.1 26.3 21.5 Dew Point exit gas, ° C.32.71 26.73 25.85 21.45

The results show that Limb A has low total condensation, but a very highdew point. This increases the opportunity for condensation outside thelimb, e.g., in the ventilator. Limbs B and C had much lower dew pointsfor the exit gas than Limb A, but the total condensation wasunacceptably high. The Limb D (the multi-lumen limb) had the lowestcondensation of all samples, and the lowest dew point for the exit gas.Thus, Limb D had the lowest opportunity for condensation outside thelimb in the ventilator.

The individual conduits of a multi-lumen limb 210 comprising a pluralityof individual conduits without reinforcing ribs can have an unexpectedlyhigh void fraction, while maintaining pneumatic compliance of less than10 mL/kPa/m. In certain embodiments, the conduits of a multi-lumen limbcomprising three individual conduits without reinforcing ribs have avoid fraction in the range of 40% and 50% (or in the range of about 40%and about 50%), such as 45% (or about 45%), while the overall pneumaticcompliance of the multi-lumen limb is less than 10 mL/kPa/m. This resultis unexpected, as high-void fraction foam would be expected to be weak,and a foam conduit without ribs would be expected to be weaker still.Thus, one would ordinarily expect excessively high pneumatic compliancewith such a configuration. As shown in Table 3, despite the higher voidfraction and lack of reinforcing ribs in the component conduits, themulti-lumen limb has pneumatic compliance similar to that of the Evaqua2™ limb, a corrugated, rib-reinforced, single-lumen foam limb, having avoid fraction of 35%±4%.

Table 3 compares the pneumatic compliance of a multi-lumen sample andsingle-lumen limb samples. All of the conduits/limbs are formed of thesame foam material, as described in PCT Publication WO 2011/077250.Limbs A-C are adult Evaqua 2™ limbs having reinforcing ribs, and thefoam material has a void fraction of 0.35. Limb D is a three-lumen limbcomprising three infant-size conduits without reinforcing ribs, and thefoam material has a void fraction of 0.448.

TABLE 3 PNEUMATIC COMPLIANCE Limb Average compliance, mL/kPa/m A 2.74 B2.51 C 2.69 D 2.61

As shown in Table 3, although the individual conduits of Limb D do nothave reinforcing ribs, Limb D has a pneumatic compliance comparable tothat of Limbs A-C.

The limbs 210 illustrated in FIGS. 13 and 14 illustrate activeapproaches to temperature control in conjunction with the multi-lumendesigns of FIG. 11A-11D. FIG. 13 illustrates a limb 210 with across-section similar to the limbs 210 illustrated in FIG. 11D and aheater wire 212 with varying pitch spacing along its length, similar tothe limbs described with reference to FIGS. 6 and 10 .

Heater wires 212 can be used to limit the cooling of the gas that mayarise due to excessively low external temperature. FIG. 14 illustrates alimb 210 with a multi-lumen design in conjunction with heater wires 212in each individual conduit 211. The heater wire 212 can extend generallylongitudinally along a length of individual conduit 211. For example, asshown in FIG. 14 , the heater wire 212 can be spirally wound alongsubstantially the full extent of each individual conduit 211.Nevertheless, the heater wire can extend along a shorter section. Theheater wire 212 can be embedded or encapsulated in the wall of theindividual conduit 211 or disposed inside the lumen. The heater wire 212in FIG. 11 has a variable pitch. Alternatively, in spiral-woundconfigurations, the heater wire can have a regular pitch. Other suitableheater wire configurations are known in the art and are contemplatedwithin the scope of this disclosure.

FIG. 15 illustrates various multi-lumen configurations for a limb 210.As discussed above, the individual conduits 211 can be twisted aroundeach other for mechanical stability and/or support. By twisting theindividual conduits, each conduit's length is greater than the length ofthe resulting limb 210. This can increase the residence time the gasspends in the limb at constant volumetric flow rate, which can result ina more advantageous temperature profile, breathability, and reduction inrain out. In some embodiments, the multiple individual conduits 211 canbe held together using adhesives. In some embodiments, the multipleindividual conduits can be held together using securing mechanisms 215such as clips, rubber bands, ties, or the like. In some embodiments, theindividual conduits can be held together using a sheath 214, where thesheath 214 can also be insulating and/or the sheath 214 can be configureto be aesthetically pleasing. The number of twisted conduits can be, forexample, 2, 3, 4, 5, or more than 5. In at least one embodiment, thelimb 210 comprises three conduits.

FIG. 16 shows an example securing mechanism 215 suitable for use with athree-conduit configuration for a limb. In this example, the securingmechanism 215 comprises a plurality of rings arranged in a trefoil. Thesecuring mechanism 215 trefoil shown in FIG. 16 can be formed from anextruded plastic, metal, or foam material.

To assemble a limb as shown in FIG. 15 , each of the three conduits 211can be passed through one of the rings of a first securing mechanism 215trefoil, shown in FIG. 16 , and then twisted or braided. The threeconduits 211 can then be passed through the rings of a second securingmechanism 215 trefoil placed at a desired distance from the firstsecuring mechanism 215 trefoil, and then twisted or braided again. Thethree conduits 211 can then be passed through the rings of a thirdsecuring mechanism 215 trefoil placed at a desired distance from thesecond securing mechanism 215 trefoil, and twisted or braided yet again.The three conduits 211 need not be twisted or braided after passingthrough a securing mechanism 215 trefoil, however, if a looserconfiguration is desired. For example, the twisting or braiding can beeliminated after the three conduits 211 are passed through the rings ofthe second securing mechanism 215 trefoil. The twisting or braiding canalso be eliminated entirely. In addition, when a tighter configurationis desired, the three conduits 211 can be twisted or braided multipletimes between securing mechanisms 215. The method described herein doesnot imply a fixed order to the steps. Nor does it imply that any onestep is required to practice the method. Embodiments may be practiced inany order and combination that is practicable.

Suitable spacing for the securing mechanism 215 trefoil can be in therange of 150 mm and 500 mm (or in the range of about 150 mm and about500 mm), such as 250 mm or thereabout. In some embodiments, a pluralityof securing mechanisms 215, for example, a number in the range of 2 and9, such as 2 or 3, can be placed along a commercially-standard length oftubing. Desirably, the securing mechanisms 215 are evenly or aboutevenly spaced from each other and from both ends. For example, when twosecuring mechanisms 215 are used, the one securing mechanisms can beplaced at the ⅓ length position and one securing mechanism can be placedat the ⅔ length position. Two securing mechanism 215 can be spaced 500mm (or about 500 mm) apart. Nine securing mechanisms 215 can be spaced150 (or about 150 mm) apart. Fewer securing mechanisms can be employedin a twisted or braided configuration.

The foregoing spacing configurations have been found to prevent theindividual conduits from separating, while not significantly reducingbreathability. It was also discovered that, when the securing mechanism215 trefoils are placed sufficiently close together (e.g., at a spacingof about 250 mm), the corrugation on the outside of the conduit 211creates enough friction that the twists does not easily untwist. It wasfurther discovered that the number of securing mechanisms 215 holdingthe individual conduits 211 together does not significantly impact theoverall compliance of the limb. Table 4 shows the results of compliancetesting for a three-conduit 211 limb configuration with different numberof securing mechanism 215 trefoils. By way of comparison, Table 5provides results of compliance testing for single conduit limbs. All ofthe conduits/limbs described in Tables 4 and 5 formed of the same foammaterial, as described in PCT Publication WO 2011/077250. The limb inTable 4 is a three-lumen limb comprising three infant-size conduitswithout reinforcing ribs, and the foam material has a void fraction of0.448. The “adult” limb in Table 5 is a 24-mm-outer-diameter Evaqua 2™limb having reinforcing ribs, and the foam material has a void fractionof 0.35. The “infant” limb in Table 5 is a 15-mm-outer-diameter Evaqua2™ limb without reinforcing ribs, and the foam material has a voidfraction of 0.448.

TABLE 4 PNEUMATIC COMPLIANCE AS A FUNCTION OF NUMBER OF SECURINGMECHANISMS No. of Volume Average Securing Infused, Pressure, Volume/compliance, Mechanisms mL kPa Pressure Ratio mL/kPa/m 1 36.69 5.997 6.124.08 2 37.589 6.148 6.11 4.08 3 35.887 6.006 5.98 3.98 4 36.105 6.0465.97 3.98 5 36.427 6.044 6.03 4.02

TABLE 5 PNEUMATIC COMPLIANCE OF SINGLE CONDUIT LIMBS Volume AverageInfused, Pressure, compliance, Limb mL kPa mL/kPa/m Adult 32.022 6.0273.54 Infant 12.180 6.048 1.34

The above-described trefoil shape is provided as an example. A differentnumber of conduits 211 will necessitate a different number of rings. Forexample, a securing mechanism 215 comprising four rings arranged in aquatrefoil can be used with a four-conduit configuration; a securingmechanism 215 comprising five rings arranged in a cinquefoil can be usedwith a five-conduit configuration; and so forth. In addition, while theforegoing examples describe generally symmetrical multi-lobed shapes,asymmetrical configurations of the rings are also contemplated.

FIGS. 17A-17E show a three-way connector 301 suitable for use on one orboth ends of a three-lumen limb 210. The connector 301 is preferably amolded component formed from a suitable material such as plastic, suchas polypropylene or polytetrafluoroethylene.

The three-way connector 301 comprises a unitary portion 305 and atripartite portion 307. The unitary portion 305 comprises a conduitsuitable for connecting to port of a device, such as a humidifier or apressurized gas source, or to a port of a patient interface, such as anasal cannula, a face mask, a nasal mask, a nasal/pillow mask.Desirably, the conduit of the unitary portion 305 has a standard-sizemedical taper suitable for use with the desired device or patientinterface. As shown in greater detail in FIG. 17E, the tripartiteportion 307 comprises three conduits 311 each suitable for connecting toa conduit 211.

As shown in FIGS. 17C and 17D, the three-way connector 301 can comprisean internal ogive 315. As used herein, ogive is defined to mean atapered, streamlined, three-dimensional object generally resembling abullet or torpedo. In FIGS. 17C and 17D, the leading edge of the ogive315 is pointed. Nevertheless, the term is used herein in its broadestsense and encompasses shapes having a pointed, rounded, or blunt leadingedge, and includes without limitation cones, pyramids or tetrahedrons,truncated cones, truncated pyramids or tetrahedrons, and other truncatedogives. The base (widest portion) of the ogive 315 is situated proximalthe tripartite portion 307. The ogive 315 tapers in the direction of theunitary portion 305. The ogive 315 can more evenly divide the gas flowfrom the unitary portion 301 into the three conduits 311 of thetripartite portion 307. The ogive 315 can also more evenly combine gasflow from the three conduits 311 of the tripartite portion 307 as thegas flow enters the unitary portion 301 and promote laminar flow.

CONCLUSION

Examples of various limbs for use with medical circuits have beendescribed with reference to the figures. The representations in thefigures have been presented to clearly illustrate principles describedherein, and details regarding divisions of modules or systems have beenprovided for ease of description rather than attempting to delineateseparate physical embodiments. The examples and figures are intended toillustrate and not to limit the scope of the embodiments describedherein. For example, the principles herein may be applied to limbs foruse in other circuits as well as respiratory circuits, includingsurgical humidifiers.

As used herein, the term “processor” refers broadly to any suitabledevice, logical block, module, circuit, or combination of elements forexecuting instructions. For example, the controller 122 can include anyconventional general purpose single- or multi-chip microprocessor suchas a Pentium® processor, a MIPS® processor, a Power PC® processor, AMD®processor, ARM® processor, or an ALPHA® processor. In addition, thecontroller 122 can include any conventional special purposemicroprocessor such as a digital signal processor. The variousillustrative logical blocks, modules, and circuits described inconnection with the embodiments disclosed herein can be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.Controller 122 can be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

Data storage can refer to electronic circuitry that allows information,typically computer or digital data, to be stored and retrieved. Datastorage can refer to external devices or systems, for example, diskdrives or solid state drives. Data storage can also refer to fastsemiconductor storage (chips), for example, Random Access Memory (RAM)or various forms of Read Only Memory (ROM), which are directly connectedto the communication bus or the controller 122. Other types of memoryinclude bubble memory and core memory. Data storage can be physicalhardware configured to store information in a non-transitory medium.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments. As used herein, the terms “comprises,”“comprising,” “includes,” “including,” “has,” “having” or any othervariation thereof, are intended to cover a non-exclusive inclusion. Forexample, a process, method, article, or apparatus that comprises a listof elements is not necessarily limited to only those elements but mayinclude other elements not expressly listed or inherent to such process,method, article, or apparatus. Also, the term “or” is used in itsinclusive sense (and not in its exclusive sense) so that when used, forexample, to connect a list of elements, the term “or” means one, some,or all of the elements in the list. Conjunctive language such as thephrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be either X, Y or Z. Thus, suchconjunctive language is not generally intended to imply that certainembodiments require at least one of X, at least one of Y and at leastone of Z each to be present.

It should be emphasized that many variations and modifications may bemade to the embodiments described herein, the elements of which are tobe understood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.Further, nothing in the foregoing disclosure is intended to imply thatany particular component, characteristic or process step is necessary oressential.

What is claimed is:
 1. A multi-lumen expiratory limb, the multi-lumenexpiratory limb comprising: a first securing mechanism comprising afirst plurality of interconnected lobes; and a plurality of breathableconduits each having a lumen, wherein each breathable conduit of theplurality of breathable conduits extends through a different lobe of thefirst securing mechanism, the first securing mechanism being spaced froma first end of the multi-lumen expiratory limb and the first securingmechanism being spaced from a second end of the multi-lumen expiratorylimb; wherein the first securing mechanism is configured to prevent eachbreathable conduit of the plurality of breathable conduits fromseparating away from an adjacent conduit of the plurality of breathableconduits while also spacing each breathable conduit of the plurality ofbreathable conduits enough from the adjacent conduit for maintainingbreathability of each breathable conduit.
 2. The multi-lumen expiratorylimb of claim 1, further comprising a second securing mechanismcomprising a second plurality of interconnected lobes, wherein eachbreathable conduit of the plurality of breathable conduits extendsthrough a different lobe of the second securing mechanism.
 3. Themulti-lumen expiratory limb of claim 2, wherein the plurality ofbreathable conduits are braided or twisted between the first securingmechanism and the second securing mechanism.
 4. The multi-lumenexpiratory limb of claim 3, wherein the plurality of breathable conduitsare braided or twisted a plurality of times between the first securingmechanism and the second securing mechanism.
 5. The multi-lumenexpiratory limb of claim 2, wherein the first securing mechanism isspaced from the second securing mechanism by between 150 mm and 500 mm.6. The multi-lumen expiratory limb of claim 2, wherein the firstsecuring mechanism is spaced from the second securing mechanism by about250 mm.
 7. The multi-lumen expiratory limb of claim 2, wherein spacingbetween the first securing mechanism and the second securing mechanismis configured to be adjusted for loosening or tightening spacing betweenconduits of the plurality of breathable conduits.
 8. The multi-lumenexpiratory limb of claim 2, further comprising: a third securingmechanism comprising third plurality of interconnected lobes; whereineach of the plurality of breathable conduits extends through a differentlobe of the third securing mechanism; and wherein the plurality ofbreathable conduits are braided or twisted between the second securingmechanism and the third securing mechanism.
 9. The multi-lumenexpiratory limb of claim 8, wherein the first securing mechanism, thesecond securing mechanism, and the third securing mechanism are equallyspaced along a length of the plurality of breathable conduits from oneanother and from ends of the plurality of breathable conduits.
 10. Themulti-lumen expiratory limb of claim 1, wherein the first securingmechanism is formed from extruded plastic.
 11. The multi-lumenexpiratory limb of claim 1, wherein the first securing mechanism isformed from metal.
 12. The multi-lumen expiratory limb of claim 1,wherein the first securing mechanism is formed from a foam material. 13.The multi-lumen expiratory limb of claim 1, wherein the first securingmechanism is arranged as one of a trefoil, a quatrefoil, and acinquefoil.
 14. The multi-lumen expiratory limb of claim 1, whereinlobes of the first securing mechanism are arranged symmetrically arounda center.
 15. The multi-lumen expiratory limb of claim 1, wherein lobesof the first securing mechanism are arranged asymmetrically around acenter.
 16. The multi-lumen expiratory limb of claim 1, wherein thefirst securing mechanism comprises three interconnected lobes.
 17. Themulti-lumen expiratory limb of claim 1, wherein the first securingmechanism comprises a sheath configured to hold the plurality ofbreathable conduits generally together.
 18. The multi-lumen expiratorylimb of claim 17, wherein the sheath comprises an insulating material.19. A multi-lumen expiratory limb, the multi-lumen expiratory limbcomprising: a plurality of breathable conduits each having a lumen; afirst securing mechanism comprising a first plurality of interconnectedlobes, the first securing mechanism being arranged as one of a trefoil,a quatrefoil, and a cinquefoil, each breathable conduit of the pluralityof breathable conduits extending through a different lobe of the firstsecuring mechanism; a second securing mechanism comprising a secondplurality of interconnected lobes, each breathable conduit of theplurality of breathable conduits extending through a different lobe ofthe second securing mechanism; the plurality of breathable conduitsbeing braided or twisted between the first securing mechanism and thesecond securing mechanism; and the first securing mechanism beingconfigured to prevent each breathable conduit of the plurality ofbreathable conduits from separating away from an adjacent conduit of theplurality of breathable conduits while also spacing each breathableconduit of the plurality of breathable conduits enough from the adjacentconduit for maintaining breathability of each breathable conduit.
 20. Amulti-lumen expiratory limb, the multi-lumen expiratory Jimb comprising:a plurality of breathable conduits each having a lumen; a first securingmechanism comprising a first plurality of interconnected lobes, eachbreathable conduit of the plurality of breathable conduits extendingthrough a different lobe of the first securing mechanism; and the firstsecuring mechanism being configured to prevent each breathable conduitof the plurality of breathable conduits from separating away from anadjacent conduit of the plurality of breathable conduits while alsospacing each breathable conduit of the plurality of breathable conduitsenough from the adjacent conduit for maintaining breathability of eachbreathable conduit.